In medical terms, a pleural effusion is an abnormal collection of liquid in the pleural cavity, which is a narrow gap between the pleurae. The liquid therefore is situated in the rib cage between the lung and the ribs.
In healthy humans, the pleural cavities are filled with a small amount—approximately 5 ml—a high-protein liquid, which, as a type of “lubrication layer”, provides freedom of movement to the lungs during inhalation and exhalation.
Smaller pleural effusions (up to a volume of approximately 500 ml) often remain unnoticed. In the case of larger pleural effusions, dyspnea occurs as cardinal symptom, at least in the case of physical exertion. This is due to a reduction in the lung capacity due to the volume taken up in the thoracic cavity by the pleural effusion. The lung is compressed and, as a result, only a smaller portion of the lung tissue is able to take part in the oxygen exchange. Suffocation of the patient may be the result in extreme cases. Therefore, larger pleural effusions are generally “drained” for relief of the patient, i.e. a pleural tap or a thoracentesis is performed, with the aid of which the liquid is discharged from the pleural cavity. By contrast, smaller pleural effusions are treated conservatively, i.e. non-invasively.
Pleural effusions may have varied causes, which may all be referred to as medically relevant. By way of example, they often occur on both sides in the case of cardiac failures; in the case of trauma or cancer, a one-sided pleural effusion can usually be observed. A pleural effusion is often a byproduct of a different disease, which may not necessarily, but only sometimes, result in pleural effusion. A treating or diagnosing practitioner may therefore not necessarily search for a pleural effusion in the case of every patient with a specific disease.
Currently, pleural effusions are usually identified only visually in medical image data as a result of the experience of diagnostic practitioners. Then, there is manual segmentation of the pleural effusion in the image data. Here, use is made, in particular, of CT image data and ultrasound image data. The volume or the extent of a pleural effusion can be established by means of an estimation method, in which a distance measurement value (the axial diameter of the rib cage up to the collapsed lung) in the thorax is multiplied by a selection of possible selectable constants. However, none of these constants were found to be sufficiently correct, and so this determination, just like the manual segmentation, is not only time-consuming but also, moreover, inaccurate.
The article Donohue, Rory/Shearer, Andrew/Bruzzi, John: “Constrained region-based segmentation of pleural effusion in thin-slice CT”. Proceedings of the 2009 13th International Machine Vision and Image Processing Conference (IMVIP '09). IEEE Computer Society, Washington D.C., pages 24-29 describes a semiautomatic methodology for distinguishing between tumors and pleural effusions. Here—proceeding from a start point entry by a user—a region growing method is performed. Thus, a user input is necessary here.
Against this background, it is an aspect to provide an alternative option, with the aid of which a potential pleural effusion is identified, in particular automatically and as reliably as possible. Furthermore, it is preferably also an aspect to enable an improved determination of the dimensions of an identified potential pleural effusion.